Genes are the basic units of heredity that determine the traits and characteristics of an organism. They come in pairs, with one allele inherited from each parent. Here's a brief explanation of dominant and recessive genes:

Dominant gene: A dominant gene is a gene that expresses its trait whenever it is present in an individual's genotype, even if only one copy is present. This means that if an individual inherits one dominant allele and one recessive allele for a particular gene, the dominant allele will be expressed and determine the phenotype. Dominant genes are typically represented by uppercase letters, such as "D".

Recessive gene: A recessive gene is a gene that is only expressed when two copies of the gene are present in an individual's genotype. This means that if an individual inherits two copies of the recessive allele for a particular gene, the recessive allele will be expressed and determine the phenotype. If an individual inherits only one copy of the recessive allele and one copy of the dominant allele for a particular gene, they will not express the recessive trait, but will be a carrier for that trait. Recessive genes are typically represented by lowercase letters, such as "d".

In summary, dominant genes are genes that are always expressed whenever they are present in an individual's genotype, while recessive genes are only expressed when two copies of the gene are present. An individual's phenotype is determined by the expression of their genes, which can be influenced by both dominant and recessive alleles.